Why is it not possible to locate the epicentre of an earthquake using a single seismograph?
A single seismograph will detect an earthquake and tell you roughly how far away it is from the seismograph. However this could be in any direction. Two seismographs will give you two possible locations for the earthquake. Only by including a thrid seismograph are you able to pinpoint the location of the quake. This image shows you how it works: http://servercc.oakton.edu/~billtong/eas100lab/epicenter3.gif A, B and C are the seismographs and the black dot where all 3 circles cross is the epicenter (location) of the earthquake. Without B and C it would be impossible to tell where the earthqauke was on A’s circle. With just A and B you get much closer but it could be at the real location or at the second point where the two circles cross. 3 seismographs is the absolute minimum but in practise many seismographs are used and inlcuding more in your attempt to locate an earthquake will give much greater detail.
